In recent years the importance of economics for competition law and policy has steadily increased. As a result, the issue of an effective integration of economics into competition law enforcement has gained prominence. This paper argues that the most relevant issues and challenges in this context are best encapsulated by the term forensic economics in competition law enforcement. Expert economic opinions constitute one specific input channel for forensic economics in competition law proceedings. In order to contribute effectively to better informed decisions, expert submissions, however, have to conform to certain minimum quality standards such as those laid down in the "Best Practices for expert economic opinions" issued by the Bundeskartellamt in October 2010. A comparative analysis of the Bundeskartellamt’s Best Practices reveals that they are broadly in line with similar guidance documents issued by competition authorities in other jurisdictions. Moreover, the court-based adversarial enforcement regime in the U.S. developed very similar principles governing the admissibility of expert testimony. Accordingly, there is a growing international consensus on minimum quality standards which should guide forensic economics in competition law enforcement in general. These can be summarized under two principles: relevance and reliability. Both are of equal importance.